1. Field of the Invention
The present invention relates to digital printer, and more specifically to a digital printer that utilizes a dye ribbon.
2. Description of the Prior Art
Digital printers are used in computer systems to print digital images. One type of printer uses a print head to heat a dye ribbon to transfer dye of different colors to a print medium. The dye ribbon comprises dyed regions colors that can be proportioned to approximate true color, and usually has a transparent overcoating region as well. Currently, this type of printer is commonly used to print digital photographs.
Consider a thermal printer 20 as shown in FIG. 1. The thermal printer 20 includes a housing 22, a thermal print head 24 mounted on a track 26 that is attached to the housing 22, and a removable ribbon cassette 28 installed in the housing and having a spooled dye ribbon 30. The printer 20 further includes motors (not shown and a control circuit (ref. 38 of FIG. 2) that drive the print head 24 and ribbon cassette 28 to print dye onto a print medium (not shown) such as a piece of paper.
Please refer to FIG. 2 showing a cross-sectional view of the printer 20 cut along a section line 2xe2x80x942 of FIG. 1. In FIG. 2 some components of FIG. 1 are omitted for clarity. The printer 20 further comprises a light source (such as an LED) 32 and a photosensor 34. The light source 32 emits light to the dye ribbon 30. Where the light passes through the ribbon 30 the light can be detected by the photosensor 34. A specific arrangement of the light source 32 and photosensor 34 establishes a specific sensing area 36 on the ribbon 30. A controller 38 controls the operation of the printer 20 by controlling the print head 24, ribbon cassette 28, light source 32, and photosensor 34. As the controller 38 controls the ribbon 30 to advance so that the print head 24 can print different colors to the print medium, a color of the ribbon 30 in the sensing area 36 changes.
Please refer to FIG. 3 showing the dye ribbon 30 removed from the ribbon cassette 28. The ribbon 30 comprises regions of printing dye separated by strips of unprintable black dye. In FIG. 3 printing dye is identified as Y for yellow, M for magenta, C for cyan, and O for transparent overcoating, while the unprintable black strips are identified as B. The sensing area 36 and print head 24 are separated by a predetermined distance. As the ribbon 30 moves relative to the sensing area 36, the photosensor 34 detects the black dye regions B and triggers the printer to set operational parameters for the next color of dye on the ribbon 30.
For example, suppose the ribbon 30 as illustrated in FIG. 3 is moving to the right, the photosensor 34 and print head 24 are stationary, and the printer 20 has just completed printing magenta dye to the print medium. The photosensor 34 detects the black strip between the yellow and magenta dye regions and automatically configures operational parameters of the print head 24 for printing yellow. That is, the black strips trigger the printer to prepare for the next color in the predetermined color sequence of the ribbon 30.
This triggering process is readily apparent in the signal diagram of FIG. 4 The signal diagram of FIG. 4 shows a plot of signal output of the photosensor 34 against a distance X along the length of the ribbon 30. The photosensor 34 is configured such that it has a low output when detecting the unprintable black dye strips and a high output when detecting any colored printing dye region.
There are several disadvantages of the prior art printer 20. These include the expense of disposing a plurality of unprintable black dye regions that are exclusively used for detection and the added length of ribbon 30 needed to accommodate the black dye regions.
It is therefore a primary objective of the claimed invention to provide a method for recognizing a color of a printing ribbon and a ribbon thereof to solve the problems of the prior art.
Briefly summarized, the claimed invention method includes providing a printing ribbon having a repeated sequence of dyed and undyed regions such that output of a photosensor sensing the ribbon is a low or high level based on a threshold. The repeated sequence is a short low level region, a first long high level region, a first long low level region, a short high level region, a second long low level region, and a second long high level region. The method includes illuminating a sensing area of the ribbon, moving the ribbon relative to the sensing area, measuring output of the photosensor over time as the ribbon moves, correlating output of the photosensor to the repeated sequence as the ribbon moves to determine the color of the ribbon under the print head, and setting operational parameters of the printer and print head according to the color of the ribbon under the print head.
According to an embodiment of the claimed invention the short low level region comprises black dye, the first long high level region comprises yellow dye and undyed ribbon, the first long low level region comprises magenta dye, the short high level region comprises undyed ribbon, the second long low level region comprises cyan dye, and the second long high level region comprises transparent overcoating and undyed ribbon.
It is an advantage of the claimed invention that the dye regions themselves are used to trigger the photosensor to allow to printer to set operational parameters for the print head and the color of dye ribbon.
It is a further advantage that no exclusive unprintable black dye regions are required to trigger the photosensor thus saving the associated manufacturing cost and time.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.